Facebook should be paying you for your pics as Shareapic would.
But why would a company pay you for sharing your pics?
I don’t know the inside story for any particular company, but I can tell you
1) there’s a load of money coming in the digital photography bust and
2) more content to more people = more advertising = more money
I don’t know any inside strategy, I can only guess why a company would NOT pay you for your content you provide.
You can continue using your current photo sharing service provider if you like, there’s nothing stopping you. There’s nothing stopping you from using as many photo sharing services as you like.